OpenJDK 12 for CentOS-based alpha Docker images

Tags: #<Tag:0x00007f49110212d0>

The default OpenJDK is now in version 12 on CentOS, therefore the next Docker images based on CentOS will be using this JDK (instead of OpenJDK 1.8).

As a first step, this will be the case only on the alpha and alpha-light images which include Simplicité version 4.0.P24a (master branch).

Please report any issue you may experience with this up-to-date OpenJDK